Polyvalent metal ion chelating agent



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2,806,060 PQLYVALENT ivmrAL ioN CHELATING AGENT No Drawing. ApplicationSeptember 3, 1954, Serial No. 454,208

3 Claims. (Cl. 260-534) This invention relates to new compoundsparticularly useful as chelating agents for trivalent and bivalent metalions, further characterized by their effectiveness in solu tions over awide range of pH.

It is a basic object of this invention to provide compounds useful forthe chelation of polyvalent metal ions in a range of pH from strongalkaline to strong acid solution.

It is another obiect of the invention to provide compounds having acidand alcohol functions within the molecule such that a polydentatechelating structure is available for the full coordination of polyvalentmetal ions.

Other objects and advantages of the invention will in part be obviousand in part appear hereinafter.

The invention accordingly is embodied in chelating agents having thefollowing essential structure:

HO (3115011: B

/NCH2CHCHr-N-XN HO CHzCHz OH R in which X is any bivalent low molecularweight alkylene radical which puts 2-3 carbon atoms between thenitrogens such as ethylene, propylene, isopropylene, 1-2 cyclohexylene,and R is selected from the group consisting of CH2COOM and CH2CH2COOM,wherein M is hydrogen, alkali metal, ammonium or substituted ammonium.

A specific compound coming within the scope of the invention isidentified chemically as N-(2-hydroXy-3-iminodiethanolpropyl) N, N, Nethylenediaminetriacetic acid (and salts), having the formula:

II I

Analysis of the structure suggests steric and structural reasons for itsversatility for it can be seen that within the compound there exists anN-(hydroxyethyl) -ethylenediamine-triacetic acid moiety bracketed andidentified with Roman numeral I, and also a fused triethanolamine moitybracketed and identified with Roman numeral 11.

Since this compound in one portion thereof has a group of acetic acidfunctions in chelating relationship with the amino nitrogens and in thesecond portion of the molecule contains a group of ethanol functionsalso in chelating relationship with the amino nitrogens, the compoundchelates bivalent metal ions very effectively including the alkalineearth metal ions in strongly acid to strongly alkaline solutions to formchelates having the structure:

R CHz-COOM wherein R represents the polyalkauolamine residue.

' atent ice t are alkaline earths, barium, strontium, magnesium-andtransition metals, such as iron and chromium.

The chelation structure with trivalent metal ions is subject to somespeculation, but it is probable that chelation occurs utilizing only thecarboxylic acid and nitrogen groups, the remaining coordinationpositions of the hexa- I coordinate metals being satisfied by water asindicated in the formula sketched below:

OH CHzCHzOH C O-CE CHz-(fH-GHz-N O --N OH CHaCHzOH Metals such as iron,chromium, cobalt, aluminum, are typical trivalent ones chelated insubstantially this fashion in solution.

In moderately alkaline solutions, that is pH 8 to 9, the hydroxyl groupof the Z-hydroxypropyl radical would probably be involved in the chelateformation to give a compound which may be represented as follows:

In caustic solutions bivalent metal ions are bound up by the acetic acidgroups and nitrogen atoms. Trivalent metal ions like iron and chromiumare bound through the triethanolamine groups so that the resultingcompound may be represented as follows:

From these indications it is apparent that compounds of this classpossess the unique property of being capable of simultaneously chelatinga trivalent metal ion and a bivalent metal ion and that in this fashiontwo moles of metal ion may be chelated per mole of chelating agent. Theefiective chelating capacity of the compound for bivalent and trivalentmetals extends over a broad range of metals including those named aswell as a broad range of pH.

Preparation of compounds corresponding to the formula may be carried outby reacting chlorohydrin and condensing the resulting product withethylenediamine and thereafter carboxymethylating. The sequence ofreactions in synthesis is listed as follows:

diethanol amine with epi- It is apparent that other methods of synthesiscan be used and that this sequence of reactions is given by way ofillustration and not of limitation.

The following examples of preparation are typical:

Example 1 One mole of N-(2-hydroxy-3-chloropropyl)-diethanolamine (211.6g.) in 250 ml. of water was added dropwise with stirring to one mole ofa 50 percent aqueous solution (120 g.) of ethylenediamine (molar ratioof 1:1) heated to slow reflux over a period of two 'hours. One mole ofsodium hydroxide (41.2 g. of 97.4 percent sodium hydroxide in 250 ml. ofwater) was added as needed to keep the pH about 10. The mixture wasrefluxed for an additional 6 hours and then evaporated to dryness invacuo. The semi-crystalline viscous yellow residue was taken up inalcohol to remove the sodium chloride and the alcohol solutionevaporated to dryness in vacuo. The viscous yellow residue was thendissolved in w'ater and carboxymethylated according to Bersworth Patent2,407,645.

The resulting clear yellow solution is an excellent chelating agent fordiand trivalent metal ions including the alkaline earth metal ions andferric ions in strongly acid to strongly caustic solutions.

Example 2 Same procedureas in Example 1 but using a molar ratio ofN-(2-hydroxy-3-chloropropyl)-diethanolamine to ethylenediamine of 1:3.

The final reaction product, a clear yellow solution,

possessed a higher chelati'on value per unit weightthan did the reactionproduct of Example 1. This Is 'due to a greater yield of theintermediate product N-(Z-hydroxyethyl3-iminodiethanolpropyl)'-ethylenediamine resulting from the greaterratio of reactants used initially.

Evaporation of the aqueous solution to dryness gave a pale semi-solidmass believed to have the formula:

The tree acid can be'isolated by treating the alkaline reaction productwith the acid form of an ion exchange (2) resin, such as, Dowex-SO, in acolumn or batch process. HOCHzCHfl From the acid solution resulting, aviscous off-white H residue is obtained upon evaporation. This productshows 7 NTOHFSJEFCHEOI'kENCHCHN z no tendency to crystallize but maywell do so upon con- HOCHZCHZ OH 5 tinued standing.

HOCH2CH2 The triethanolamine portion of the molecule may com-N-CHz-OEF-OHz-N-CH-CEk-NH; bine with fatty acids (saturated andunsaturated), sulm 6 fonated fatty acids, detergent forming acidsgenerally and a n V Hocmom NCHzCHOHzN''OHg-OHN'Hz 8NaCN 301120 3Hz0 HOGama. 0H

' noomom cHPoooNa 331E3 6 NCHz-(|3HCH2N--CH2OH2N accent. 011 cm one-000moooNs mineral acids and other acids 'to form salts analogous to thetriethanolamine salts. These products, especially those bearing fattyacids and detergent forming acids are of interest soaps, detergents andemulsions. 7

An example of the preparation of such addition com: pounds is thefollowing: V V a To 0.1 mole of the acid form of the chelating agent in50 ml. of water was added 0.1 mole of stearic acid. The mixture washeated to about8 0 C. to complete reaction. The resulting solutionfoamed readily even in the presence of metal ions and was stable towardpolyvalent metal ions over the pH range of 2-14. 7

Similar results were obtained with oleic and l2-hydroxy stearic acids.Also these same acids sulfonated gave directly parallel results.

It is apparent that in the synthesis, any alkali metal salt may beforriied by us'eof the appropriate hydroxide in the formation of thealkaline medium. This, potassium, lithium, rubidium, cesium and ammoniumsalts are readily formed. Preparation of amine salts usually is carriedout by forming the acid and then reacting with the appropriate amine.

What is claimed is:

1. Compounds corresponding to the following generic formula: 7

noonzcm n N-OHzGHCH2 N -XN noomonz OH R R wherein X is any bivalent lowmolecular weight alkylene radical that places 2-3v carbon atoms betweenthe nitrogens, and R is selected from the group consisting of CH2COOHand -CH2'CH2COOH and their alkali metal, ammonium and amine salts.

2. The compound N- (2-hydroxy-3-iminodiethan0l- V propyl)-N, N, N-ethylenediaminetriacetic acid.

3. The metal salts of the compound defined in claim 2.

References Cited in the file of this sa a UNITED STATES PATENTS Bersworth Oct. 30, 1945 Be'rsworth Jan. 7, 1947

1. COMPOUNDS CORRESPONDING TO THE FOLLOWING GENERIC FORMULA: